1. Field of the Invention
The present invention relates to a device for controlling the steering angle of a vehicle, which automatically controls the rotational angle (steering angle) of a steering shaft to assume a target value. More particularly, the invention relates to a device for controlling the steering angle of a vehicle, which features improved control precision over a wide range of steering angles.
2. Prior Art
There has heretofore been known a device for automatically controlling the steering angle of a radio-controlled vehicle for use exclusively in yard (hereinafter referred to as "radio-controlled vehicle") to assume a target angle in an attempt to improve productivity and operation efficiency by saving manpower as taught in, for example, Papers of Academic Lectures, 944, Japanese Technological Association of Automobiles, Oct., 1991.
To control the steering angle of the radio-controlled vehicle of this kind, the rotational angle of the steering shaft must be detected as an absolute value. At present, a voltage detected by a potentiometer is converted into a digital value through an A/D converter and is used as a detected angular value (hereafter an angle detection value).
Similar automatic control devices have also been taught, such as a radio-controlled device for vehicles disclosed in Japanese Unexamined Patent Publication (Kokai) No. 258822/1997 and a steering angle detecting device for vehicles disclosed in Japanese Unexamined Patent Publication (Kokai) No. 13106/1986.
However, the conventional devices disclosed in the above-mentioned publications are still not satisfactory with respect to precision for controlling the steering angle and the control response. When applied to an automatic operation controller used on an automobile road such as an expressway, for example, control performance is not-obtained to a satisfactory degree and it becomes difficult to maintain travelling within a lane.
In order to improve the steering angle control precision and the control response, furthermore, the precision for detecting the steering angle must be heightened. When it is attempted to heighten the resolution of the A/D converter by using a potentiometer, however, the device tends to become susceptible to noise making, after all, and it is difficult to improve the detection precision to a sufficient degree.
Because of lack of steering angle control precision and control response, therefore, the conventional devices for controlling steering angle of the vehicle could not be applied to automatically operating the vehicles on an automobile road.
Besides, when it is attempted to enhance the detection precision of the potentiometer by enhancing the resolution of the A/D converter from the standpoint of improving steering angle control precision and response performance, the device tends to become susceptible to noise making, and it is difficult to improve the steering angle detection precision to a sufficient degree.